1. Field of the Invention
The present invention generally relates to a method for forming a thin film in a semiconductor device circuit manufacturing process; and particularly to a method for forming a thin film, which reduces plasma damage in plasma CVD.
2. Description of the Related Art
Conventionally, as a method for forming a thin film on a semiconductor substrate, plasma CVD (chemical vapor deposition) has been used. This method forms a thin film on a semiconductor substrate by a chemical reaction caused by maintaining a pressure inside a reaction chamber; keeping a semiconductor substrate temperature by raising a temperature of a susceptor in which a resistance-heating type heater is laid buried; generating plasma discharge in a space between the susceptor and a shower plate for emitting a jet of reaction gas by applying radio-frequency power to the shower plate. Interlayer insulation films, passivation films, antireflection films and others are formed by plasma CVD.
In recent years, as miniaturization of semiconductor devices has been pursued, copper (Cu) became used in place of aluminum (Al) as a material for interconnections in order to prevent an increase in RC delays. Cu is characterized in that having excellent thermal durability and low resistance values as compared with Al. Similarly, lower dielectric constants are demanded for interlayer insulation films.
In design rules for interlayer insulation films having a thickness of 130 nm, SiOF films or TEOS oxide films having dielectric constants of approximately 3.4-3.7 have been used. With the miniaturization being pursued, low dielectric constant interlayer insulation films (low-k films) having dielectric constants of 3.0 or less have become used because a thickness of the interlayer films falls below 100 nm. Because the low-k films contain carbon in oxide film bonding, the films have a drawback of low mechanical strength as compared with TEOS oxide films. This tendency becomes clear in ultra-low-k films (ULK films) having dielectric constants of 2.4-2.7, which are used for the next-generation 65 nm rules. This mechanical strength brittleness poses a problem in the Damascene process.
The Damascene process here includes the steps of: forming a trench within a desired lead pattern; filling the trench with metal or other conductive materials; etching back or polishing the metal up to an insulation layer. Interconnections stay in the trench and are mutually insulated within the desired pattern. The Dual-Damascene process, which is a developed type of the Damascene process, includes the steps of: forming two insulation layers separated by an etch stop material; and forming a trench within an upper insulation layer. A contact-via is etched through the bottom of the trench and a downside insulation layer so as to expose a downside conductive member to be contacted. In the Damascene process, low-k films, Cu which is an interconnection material, SiC films for preventing Cu diffusion, SiC hard-mask films and others are used. In the Dual-Damascene process which provides a via layer and a trench layer, low-k films of different film types are often used for respective layers. For example, a spin-on type low-k film is used for one; a plasma type low-k film is used for the other. Semiconductor devices are configured by laminating these low-k films. In such cases, adhesion among plasma type low-k films having low mechanical strength, SiO or SiC films having high mechanical strength and spin-on type low-k films becomes a problem.
In plasma CVD, plasma damage has been a problem. Due to charge-up caused by plasma, electric charge accumulated on a semiconductor substrate flows to ground potential through a susceptor heater as leakage current. If the leakage current exceeds a certain value, a gate insulation film of a semiconductor apparatus is deteriorated or destroyed, thereby lowering a semiconductor apparatus yield rate. This is called plasma damage. Additionally, as leakage current, lateral leakage current, which depends on a surface potential distribution within a semiconductor substrate surface, also exists.
In order to improve the plasma damage problem, a method for anodizing a susceptor for the purpose of improving electrode insulation performance caused by discharge, a method for pre-coating a susceptor before the thin-film formation process for the purpose of improving the insulation performance and other methods have been proposed. These methods, however, have problems of process-gas resistance, plasma resistance and heat resistance of anodic oxide films and of exfoliation of precoat films; in order to solve these problems, methods using alloy materials excellent in corrosion resistance and resistance properties were proposed (For example, Japanese Patent Laid-open No. 1999-229185).
As an alternative method for improving the plasma damage problem, there is a method increasing a pressure as well as reducing an amount of radio-frequency plasma applied at the time of thin-film formation. This method, however, has a problem because changing the process conditions changes film properties. Conversely, if the plasma amount applied is increased, sheath voltage is increased and damage on a semiconductor substrate occurs. In order to solve this problem, a method which reduces the damage by controlling the sheath voltage without changing the plasma amount applied was invented (For example, Japanese Patent Laid-open No. 2003-45849).